This invention relates generally to communication between a multitude of signal sources and corresponding signal recipients which can locate themselves with respect to each other or with a common frame of reference.
Determining a position in a physical space is often a desired piece of information in various navigational contexts. Outdoors, Global Positioning System (GPS) is an effective way to determine the position of a device. For example, a handheld device equipped with a GPS receiver can accurately determine its position with respect to a map.
A problem with the GPS systems is that a GPS receiver relies on satellite signals reaching it in a straight line. Indoors, inside urban canyons, under canopies, etc., where signals cannot meet this constraint, a GPS system may fail. Another problem with GPS systems is that they offer only coarse positioning accuracy and require a high degree of sensitivity and sophistication in the receiver device.
The fundamental approach in GPS can be applied to indoor environments by having GPS-like transmitters in sufficient numbers and at appropriate locations. However, when applied to very simple hardware, an indoor implementation of the GPS system becomes impractical. This is mainly due to the fact that the precision time base implemented in navigation satellites are complex, expensive and power consuming.
In GPS-like navigation, a number of satellites transmit and a GPS receiver, (e.g. a mobile device) receives signals from a minimum number or “constellation” of the transmitting satellites. However, it is also possible to solve the inverse problem as well, e.g. have many fixed receiver devices that receive signals from a transmitter. In this latter case, the transmitter can be located and tracked. This approach is typically the method of choice for active indoor location systems, typically entitled Real Time Location Systems (RTLS).
In a space, open or covered, “passive” tags can be mounted at known locations. As used herein, “passive” will refer to tags and other devices that acquire their electrical power primarily by scavenging incident or ambient sources of energy, such as electromagnetic (e.g. RF, visible light, etc.), mechanical, and thermal energy. The passive tags transmit signals that are captured by a mobile receiver of a passerby. The mobile receiver can simultaneously capture signals from multiple transmitters and, by correlating the condition of the received signals, can calculate a geometric relationship between the transmitting tags and receiving handheld device. This relationship can be mapped onto an absolute frame of reference, e.g. global longitude, latitude and elevation, by knowing the actual locations of the tags (“transmitters”).
A problem with passive tags is that the energy scavenged is generally quite small. Such small amounts of energy are normally not enough to generate powerful and high performance radio carrier waves for data transmission and therefore tend to be limited in range and data capacity.
U.S. Pat. No. 7,180,421, incorporated herein by reference, describes methods and solutions for making a passive Ultra Wide Band (UWB) radio device that can be powered by incident electromagnetic energy and which communicates its data through UWB impulses. The patent does not teach how, however, teach how the communicated data can be used to locate device or to aid in the navigation through environments that deploy such radio devices.
These and other limitations of the prior art will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.